1. Field of the Invention
The present invention relates to a protein partial degradation product, a process for preparing it, and its use. More particularly, it relates to a novel protein partial degradation product obtained by degradation of a grain protein such as wheat protein, maize protein, soya bean protein, etc., a process for preparing the protein partial degradation product, and it use as a quality-improving agent for food stuffs or a surface active agent.
2. Description of the Prior Art
Hitherto, as partial degradation products of vegetable proteins, there has been known those hydrolyzed by an acid, alkali or emzyme. Further, it has been known that such partial degradation products could be obtained also by an oxidative degradation using an oxidizing agent or a reductive degradation using a reducing agent.
For instance, Ian L. Batey et al. reported on the properties and the amino acid composition of partial hydrolyzates of wheat gluten obtained by hydrolysis with an alkali or acid ("Preparation of Salt-Free Protein Products from Acid or Alkali-Treated Proteins", Food Chemistry No. 12 (1983), Pages 265-275). On the other hand, A. M. Hermansson et al. reported that partial hydrolyzates of rapeseed oil protein obtained by hydrolysis with an alkali, acid or enzyme show some degrees of solubility in water, emulsifying and forming properties ("Functional Properties of Proteins for Foods--Modification Studies on Rapeseed Protein Concentrate", Lebensmittel--Wissenschaft und--Technologie Vol. 7, No. 3 (1974), Pages 176-181).
In Japanese Unexamined Patent Publication No. Sho 50-95443, it is disclosed that the slightly acidic gluten powder obtained from wheat gluten with its acidifying treatment at pH 2.0-6.0 is superior, as an additive for food stuffs, to one obtained by treatment with a reducing agent. This Publication, however, does not disclose any specific effect of the powder as the additive. Further, it is disclosed in Japanese Unexamined Patent Publication No. Sho 60-237939 that a wheat gluten partial hydrolyzate hydrozylate obtained by hydrolysis of wheat gluten with an enzyme can be used as a substitute for caseinates in the production of imitation cheeses.
In Japanese Unexamined Patent Publication No. Sho 53-124654, there is disclosed a process for the production of processed meat by addition of a gluten hydrolyzate, which is obtained under an acidic condition with hydrochloric acid, in the form of powder.
On the other hand, it is described in Japanese Unexamined Patent Publications No. Sho 56-8665 and No. Sho 57-79849 that partial degradation products of a protein, obtained by hydrolysis with an acid or an enzyme, have a surface activate capacity.
Besides, it has been known that hydrolyzates of a protein obtained by hydrolysis with an enzyme is useful for the stabilization of whipped dessert-type products (U.S. Pat. No. 3,889,001 and U.S. Pat. No. 3,903,310).
Further, it has been reported recently that a gluten partial hydrolyzate obtained by treating wheat gluten with a pepsin-immobilized bioreactor can be utilized for improving the quality of baked cake and bread such as sponge cake (A Japanese paper "Kagaku Kogyo Jiho" issued on Jun. 25, 1987).
Thus, various investigation reports have been made as to partial hydrolyzates of vegetable proteins, and in some of them there have been given disclosures on the emulsifying capacity and the quality-improving capacity for food stuffs of the partial hydrolyzates reported therein. However, according to the result of our confirmation tests, any of the partial degradation products obtained by subjecting a representative grain protein such as wheat protein, maize protein, soya been protein, etc. to either of the above-mentioned degradation means could be used as a quality-improving agent for food stuffs or a surface active agent, but its capacity was not of satisfactory level.
On the other hand, polyhydric alcohol/fatty acid ester type surface active agents and lecithin are known as relatively safe surface active agents, and they are used in the fields of food industry and medical treatment and, particularly, used widely as a quality-improving agent for food stuffs.
For instance, the so-called polyhydric alcohol/fatty acid ester type surface active agents, such as glycerol/fatty acid ester, propylene glycol/fatty acid ester, sucrose/fatty acid ester etc. are widely used as a quality-improving agent for starchy food such as bread or noodle, as the case may be, in combination with ascorbic acid or a gluconolactone (Japanese Patent Publication No. Sho 56-42887, Japanese Unexamined Patent Publications No. Sho 55-118334 and No. Sho 55-118335). Further, it is also proposed to use the glycerol/fatty acid ester, after subjecting it to a specific treatment (Japanese Patent Publication No. Sho 59-41379).
Glycerol/fatty acid ester and sucrose/fatty acid ester are frequently used as a quality-improving agent for animal proteinic food stuffs using fish or meat as the main material, such as boiled fish paste, ham, sausage, hamburger, fried ball of mincemeat, etc., and also for vegetable proteinic food stuffs using soya bean protein, wheat gluten and the like as the main material, such as bean-curds, etc. (Japanese Unexamined Patent Publication No. Sho 53-79058, No. Sho 43-8685 and No. Sho 58-89146).
Polyhydric alcohol/fatty acid ester type surface active agents and lecithin are widely used as a quality-improving agent for creamy processed milk products such as coffee whitener, whip cream, ice cream, etc. (Japanese Patent Publications No. Sho 54-39459 and No. Sho 51-9823).
Further, polyhydric alcohol/fatty acid ester type surface active agents and lecithin are used as a quality-improving agent or emulsion-stabilizer for water-in-oil emulsion type food stuffs such as margarine, shortening, etc., and oil-in-water emulsion type food stuffs such as dressing, etc. (Japanese Patent Publications No. Sho 51-17150 and No. Sho 57-58898).
However, the above-described surface active agents, polyhydric alcohol/fatty acid esters and the like, are chemical synthetic products in themselves and accordingly their toxicity is uncertain, although they are approved as food additives. Moreover, these surface active agents are not necessarily satisfactory with respect to the cost and the quality-improving effect.
Under such circumstances, we have made various investigations and have found the fact that a hydrolyzate obtained by a two or more-step degradation treatment consisting of a combination of an indispensable hydrolysis treatment with alkali by conventional means with one or more degradation treatments with any of acid, enzyme, oxidizing agent and reducing agent (i) is novel which is different from known hydrolyzates and (ii) has a surface activate capacity such as an emulsifying capacity or a surface tension-reducing capacity, and a quality-improving capacity for food stuffs, which are significantly superior to those of known hydrolyzates and equal to, or higher than, those of the above-mentioned sucrose/fatty acid esters or lecithin, and further a good particles-dispersing capacity.